The heat pipe heat transfer system; wherein, in a sealed tube having a thermal transfer location at each end, a fluid undergoes multiple heat transfer mechanisms, such as evaporation, condensation and capillary action, inside the sealed tube, providing a highly efficient transfer of heat from one end to the other; has been used in the art in various applications. One serious limitation heretofore has been that a single sealed tube, however efficient the heat pipe is and however good the thermal transfer is at each end, does not lend itself very well to heat transfer between hinged portions of a container.
The limitation becomes even more of a consideration in some electronic apparatus where the sources of heat generation are becoming more concentrated such as with semiconductor chips, the packaging is becoming tighter due to weight and size for portability, and the packaging may have a hinge connecting essential parts of the heat disposal apparatus. As specifications in one portion of an apparatus become more rigorous, the flexibility in materials and structural arrangement in other portions of the apparatus take on increased importance.
The situation is illustrated in computers, particularly of the types known in the art as laptop or notebook. In these devices, efforts have been directed to providing as many features as possible in a small and light weight package.
The most efficient and physically rugged universal package that has evolved in the art is one in which the display screen portion is hinged on a base portion supporting a keyboard, away from the user; so that it can be positioned in the direct view of the user and in an essentially vertical position with respect to the keyboard when in use and can be folded down over the keyboard when not in use.
The thermal dissipation requirements of apparatus such as the electronic apparatus in portable computers are steadily becoming greater because of increasing processor performance and the addition of features, such as modems and audio capabilities. The increasing dissipation requirements are producing situations where heat generated locally must be dissipated over larger and remote areas unrelated to the portion of the package structure where it originated.
Electromechanical means such as fans can be helpful but carry considerations in packaging for the air flow, consume power and are noisy. In the problem, the main source of the heat, is usually a very compact element such as a semiconductor processor. There is seldom much flexibility in locating such heat sources as a processor. In dissipating heat, convection and radiation from surfaces that have a broad area and are vertical such as the area behind the display is usually more effective than horizontal surfaces such as the case for the base where the processor is usually located. As specifications on weight and performance become more demanding the need increases for an ability to be flexible in materials, in material and dimensional property selection, and in structural arrangements in thermal transfer in, the packaging.
The heat pipe principle, where a pipe with both ends sealed containing a relatively volatile fluid, has one end attached with minimum thermal loss at the heat source, and the other end attached with minimum thermal loss at a heat dissipator, transfers heat very efficiently by having the fluid boil at the heat source, condense at the dissipator and return inside the pipe to the heat source. Heat transfer rates greater than 100 times the conductivity of copper can be achieved with this transfer principle.
While there have been efforts in the portable computer art to apply the heat pipe principal in heat transfer from a semiconductor processor to a heat dissipator mounted behind the display, problems in connection with the hinge have resulted in less than satisfactory results.
In U.S. Pat. No. 5,588,483 a portion of the heat dissipator is wrapped around the heat pipe which has a portion positioned along the centerline of the hinge with thermal grease being used for heat transfer and as a lubricant for the movement of the dissipator around the heat pipe each time the cover is opened and closed.
In U.S. Pat. No. 5,646,822 the heat pipe transfer is achieved with two separate heat pipes, one from the heat source to the hinge and the other from the hinge to the dissipator wherein the heat pipe ends are positioned in a cylinder aligned along the hinge centerline and a thermal grease is relied on for heat transfer and for reducing friction.